This invention generally relates to a photographic camera and more particularly, to a lens extension and retracting mechanism for use in a photographic camera of a folding type.
Conventionally, there have been proposed several lens extension and retracting mechanisms for folding type photographic cameras, for example, as shown in FIGS. 1(a) and 1(b) which are so arranged that a link system 3, 3 guides a lens board 1 for supporting a photographic lens thereon between a photographing position A (FIG. 1(a)) at a forward portion of a body of the camera and an accommodating position B (FIG. 1(b)) inside the camera body for selective extension or retraction of the lens board 1 with respect to the camera body.
In the known lens extension and retracting mechanism as described above, however, since opposite ends of the links 3a, 3a at the side of the lens board 1 have been respectively pivoted to corresponding ends of links 3b, 3b at the side of the camera body, and also to the lens board 1 so that they form a trapezoid link system in the conventional camera of this kind, there is such a disadvantage that accurate positioning is difficult to achieve, thus making it impossible to hold the lens board 1 stably and positively.
Moreover, this has been such a problem that particularly in the case where it is necessary to increase the amount of extension of the lens board 1 in a large-sized camera and the like, the length l' of each of the links 3 must be made long, and therefore, the amount of protrusion W of the links 3 towards opposite sides in the accommodated position in the camera body is undesirably increased, thus necessitating increase in lateral width W of the camera body 2, with a consequent large size to the photographic camera.
Furthermore, in the conventional arrangement as described so far, there is another disadvantage that, since rotative directions of the links 3b, 3b substantially agree with the extending direction of the lens board 1 and a component force for extending the lens board 1 forwardly is, at an initial stage of the extension of the lens board 1, a large force is required for operating a lever for said extension.